Fuel production system

ABSTRACT

A fuel production system and has an object to provide a fuel production system that is capable of producing HC with high efficiency by using variable energy. A first device is a CO/H 2  generating device that simultaneously generates CO and H 2  by performing electrolysis on CO 2  and water. A second device is a H 2  generating device that generates H 2  by performing electrolysis on water. When electric power derived from natural energy is used, the first device is seriously affected by its variation. Therefore, a steady-state portion of generated electric power (straight line in a figure) is supplied to the first device while the remaining variable portion (the portion above the straight line) is supplied to the second device.

TECHNICAL FIELD

The present invention relates to a fuel production system. Morespecifically, the present invention relates to a fuel production systemthat synthesizes fuel from electrolytically-generated H₂ and CO.

BACKGROUND ART

For example, Patent Document 1 discloses a power supply unit in whichsets priorities of three different types of electric power, namely,clean-generated power, which is generated by using sunlight or windpower as energy, fuel-cell power, which is generated by a fuel cell, andcommercial power, which is supplied from an electric power company whensupplying them to a power load system. more specifically, the powersupply unit is set to preferentially supply the clean-generated power.And the power supply unit additionally supplies the fuel-cell power andcommercial power if the clean-generated power is not sufficient to meetpower demand of the power load system. This makes it possible to mainlyuse the clean-generated power as the energy of the power load system,thereby establishing a system that minimizes the influence upon theenvironment.

For example, Patent Document 2 discloses a system in which produceshydrocarbon (HC) fuel by reacting CO and H₂ to Fischer-Tropsch reaction(FT reaction). For example, Patent Document 3 discloses an electrolyticcell comprising an oxygen-ion-conductive film made of a solid oxideelectrolyte, and a cathode and an anode disposed on both surface of thefilm respectively, generating CO and H₂ simultaneously by using theelectrolytic cell, recovering the generated source gases from theelectrolytic cell, and producing HC by reacting the recovered sourcegases to FT reaction.

RELATED ART LITERATURE Patent Documents

Patent Document 1: JP-A-2004-120903

Patent Document 2: JP-A-2008-533287

Patent Document 3: JP-A-2009-506213

Patent Document 4: JP-A-9-85044

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

A combination of technologies described in Patent Documents 1 and 3makes it possible to preferentially use the clean-generated power andproduce HC by simultaneously generating CO and H₂ as needed for FTreaction. Meanwhile, in a region where a power supply infrastructure isinadequate (e.g., in a desert region), sufficient commercial power maynot be available. The technology described in Patent Document 1 usesfuel-cell power in addition to commercial power. However, the fuel-cellpower is generated by using H₂ that is obtained when midnight power,that is, surplus commercial power, is used to perform electrolysis onwater. In other words, the fuel-cell power is generated on thepresumption that the commercial power is available. Therefore, ifsufficient commercial power is not available, the aforementioned CO andH₂ have to be generated by using the clean-generated power only.

In general, however, natural energy such as the energy from sunlightvaries. It means that generated electric power varies. Therefore, if anattempt is made to simultaneously generate CO and H₂ with anelectrolytic cell described in Patent Document 3 by using only theelectric power derived from natural energy, the generation of CO and H₂becomes unstable. When the generation of CO and H₂ is unstable, theefficiency of FT reaction, which uses the generated CO and H₂, maydecrease.

The present invention has been made to solve the above problem. Anobject of the present invention is to provide a fuel production systemthat is capable of producing HC with high efficiency by using variableenergy.

Means for Solving the Problem

To achieve the above mentioned purpose, a first aspect of the presentinvention is a fuel production system comprising:

a power generating device that generates variable electric power;

a power distribution device that is connected to the power generatingdevice to distribute electric power to a plurality of electrical loads;

a mixed gas generating device that is one of the electrical loads andperforms electrolysis on water and carbon dioxide upon receipt ofelectric power distributed by the power distribution device to generatea mixed gas made of hydrogen and carbon monoxide; and

a control device that controls the power distribution device so as tosupply predetermined electric power to the mixed gas generating device,wherein the predetermined electric power is lower than the minimum powergenerated by the power generating device within a preselected period oftime.

A second aspect of the present invention is the fuel production systemaccording to the first aspect, further comprising:

a mixed gas storage device that is connected to the mixed gas generatingdevice to store the mixed gas; and

a feedback control device that provides feedback control of thepredetermined electric power to ensure that the substance quantity ratiobetween hydrogen and carbon monoxide in the mixed gas storage devicecoincides with a preselected ratio.

A third aspect of the present invention is the fuel production systemaccording to the first or the second aspect, further comprising:

a hydrogen generating device that is one of the electrical loads andgenerates hydrogen upon receipt of electric power distributed by thepower distribution device; and

a hydrogen power generating device that generates electric power byusing hydrogen generated by the hydrogen generating device.

A forth aspect of the present invention is the fuel production systemaccording to the third aspect,

wherein, if the electric power generated by the power generating deviceis lower than the predetermined electric power while the control devicecontrols the power distribution device to supply the predeterminedelectric power to the mixed gas generating device, the hydrogen powergenerating device supplies the generated electric power to the powerdistribution device.

A fifth aspect of the present invention is the fuel production systemaccording to any one of the first to the forth aspects, furthercomprising:

a charge/discharge device that is one of the electrical loads andcapable of charging and discharging electric power distributed by thepower distribution device; and

a mixed gas generating device that generates a mixed gas made ofhydrogen and carbon monoxide by performing electrolysis on water andcarbon dioxide by using electric power from the charge/discharge device.

A sixth aspect of the present invention is the fuel production systemaccording to any one of the first to the fifth aspects, furthercomprising:

a carbon dioxide supply device that is one of the electrical loads,recovers carbon dioxide from atmospheric air upon receipt of electricpower distributed by the power distribution device, and supplies therecovered carbon dioxide to the mixed gas generating device.

A seventh aspect of the present invention is the fuel production systemaccording to the sixth aspects,

wherein the carbon dioxide supply device includes a carbon dioxiderecovery device that contains an electrolytic solution having carbondioxide absorption characteristics.

An eighth aspect of the present invention is the fuel production systemaccording to the seventh aspect,

wherein the carbon dioxide supply device includes an atmospheric airintroduction device that introduces atmospheric air into the carbondioxide recovery device, and a liquid supply device that supplies theelectrolytic solution in the carbon dioxide recovery device to the mixedgas generating device.

A ninth aspect of the present invention is the fuel production systemaccording to the seventh aspect, further comprising:

an electrolytic solution storage device that is disposed downstream andupward of the carbon dioxide recovery device to temporarily store anelectrolytic solution discharged from the mixed gas generating device;

a hydraulic power generation device that includes a turbine rotated byan electrolytic solution dropped from the electrolytic solution storagedevice, causes the rotated turbine to generate electric power, and ifthe electric power generated by the power generating device is lowerthan the predetermined electric power, supplies the generated electricpower to the power distribution device; and

a liquid supply device that supplies the electrolytic solution droppedfrom the electrolytic solution storage device to the mixed gasgenerating device.

A tenth aspect of the present invention is the fuel production systemaccording to the seventh aspect,

wherein the carbon dioxide supply device includes a carbon dioxideabsorption/regeneration device that is positioned upstream of the carbondioxide recovery device, and contains an absorbent that has carbondioxide absorption characteristics, discharges absorbed carbon dioxidewhen heated, and regenerates the carbon dioxide absorptioncharacteristics when watered.

An eleventh aspect of the present invention is the fuel productionsystem according to the seventh aspect,

wherein the carbon dioxide supply device includes a rotating electricalmachine disposed upstream of the carbon dioxide recovery device; and

wherein the rotating electrical machine includes a turbine, functions asa pressure pump that lets the turbine rotate to compress carbon dioxideand introduce the compressed carbon dioxide into the carbon dioxiderecovery device, and if the electric power generated by the powergenerating device is lower than the predetermined electric power,functions as a power generator that generates electric power by allowingthe compressed carbon dioxide in the carbon dioxide recovery device torotate the turbine in a reverse direction and supplies the generatedelectric power to the power distribution device.

A twelfth aspect of the present invention is the fuel production systemaccording to any one of the first to the eleventh aspects,

wherein the power generating device includes at least one of a solarphotovoltaic power generation device, a solar thermal power generationdevice, a wind power generation device, a tidal power generation device,and a geothermal power generation device.

Advantages of the Invention

According to the first to twelfth aspects of the present invention, thepredetermined power, which is lower than the minimum power generated bythe power generating device within the predetermined period of time, canbe supplied to the mixed gas generating device. The predetermined powercorresponds to steady-state power that remains unaffected by variation,which is a portion of electric power generated by the power generatingdevice within the predetermined period of time. When such steady-statepower can be supplied to the mixed gas generating device, CO and H₂ canbe steadily generated. When CO and H₂ are steadily generated, HC can beproduced by allowing the FT reaction to progress efficiently. This makesit possible to produce HC with high efficiency by using variable energy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a systemaccording to a first embodiment.

FIG. 2 shows (A) a relationship between a WE voltage relative to the REand a generation ratio between CO and H₂ in a first device 12, and (B) arelationship between the WE voltage relative to the RE and the energyefficiency in the first device 12 respectively.

FIG. 3 shows (A) a relationship between a WE voltage relative to the REand a generation ratio between CO and H₂ in a second device 14, and (B)a relationship between the WE voltage relative to the RE and the energyefficiency in the second device 14 respectively.

FIG. 4 shows an example of power distribution control of the firstembodiment.

FIG. 5 shows examples of mixture ratio feedback control that isexercised in a second embodiment.

FIG. 6 is a block diagram illustrating a configuration of a systemaccording to a third embodiment.

FIG. 7 shows an example of power distribution control of a forthembodiment and an example of mixture ratio feedback control of the forthembodiment.

FIG. 8 shows an example of power distribution control of a fifthembodiment.

FIG. 9 is a block diagram illustrating a configuration of a systemaccording to a sixth embodiment.

FIG. 10 is a block diagram illustrating a configuration of a systemaccording to a seventh embodiment.

FIG. 11 is a block diagram illustrating a configuration of a systemaccording to an eighth embodiment.

FIG. 12 is a block diagram illustrating a configuration of a systemaccording to a ninth embodiment.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

[Description of System Configuration]

First of all, a first embodiment of the present invention will bedescribed with reference to FIGS. 1 to 4. FIG. 1 is a block diagramillustrating the configuration of a system according to the firstembodiment of the present invention. The system shown in FIG. 1 includesa power generating device 10, which generates electric power by usingnatural energy (provides, for instance, solar photovoltaic powergeneration, solar thermal power generation, wind power generation, tidalpower generation, or geothermal power generation). The system shown inFIG. 1 also includes a first device 12 and a second device 14.

The first device 12 is a CO/H₂ generating device that simultaneouslygenerates CO and H₂ by performing electrolysis on CO₂ and water.Specifically, the first device 12 includes an electrolytic tank, aworking electrode (WE), a counter electrode (CE), a reference electrode(RE), and a potentiostat. The electrolytic tank is filled with anelectrolytic solution in which CO₂ is dissolved. The WE, the CE, and theRE are provided in the electrolytic tank. The potentiostat is configuredso that the voltage of the WE relative to the RE can be changed. Thesecond device 14 is a H₂ generating device that generates H₂ byperforming electrolysis on water. The second device 14 has the sameconfiguration as the first device 12 except that the electrolyticsolution is a mixture of water and supporting electrolyte.

Further, the system shown in FIG. 1 includes a power controldistribution device 16, which receives electric power from the powergenerating device 10 and distributes the received electric power to thefirst device 12 and the second device 14. The power control distributiondevice 16 includes a controller (not shown), which provides powerdistribution control and mixture ratio feedback control as describedlater. Furthermore, the system shown in FIG. 1 includes a CO/H₂ storagedevice 18, which stores CO and H₂ that are generated by the first device12; and a H₂ storage device 20, which stores H₂ that is generated by thesecond device 14. The CO/H₂ storage device 18 is connected to the H₂storage device 20 through a normally-closed valve (not shown), such as acheck valve or a reed valve. When the pressure within the H₂ storagedevice 20 exceeds a predetermined working pressure, H₂ in the H₂ storagedevice 20 is introduced into the CO/H₂ storage device 18.

[Electrolysis in the First Device 12]

Electrolysis reactions in the first device 12 will now be described.When the potentiostat in the first device 12 is controlled so as to flowan electric current between the WE and the CE, electrochemical reactionsoccur in the WE and the CE as indicated by formulas (1) to (3) below:WE : CO₂+2H⁺+2e ⁻→CO+H₂O   (1)2H⁺+2e ⁻→H₂   (2)CE : 2H₂O →O₂+4H⁺+4e ⁻  (3)

As indicated by formulas (1) and (2) above, CO and H₂ are simultaneouslygenerated on the WE in the first device 12. Therefore, when thegenerated CO and H₂ are collected into the CO/H₂ storage device 18 toinvoke an FT reaction, HC can be produced as an alternative to fossilfuel.

Meanwhile, the generation ratio between CO and H₂ on the WE depends onan electric current value between the WE and the CE, that is, a WEvoltage setting relative to the RE. Further, energy efficiency (theamount of heat generated by products relative to input energy, the sameshall apply hereinafter) depends on the WE voltage setting relative tothe RE. Such dependence will now be described with reference to FIGS.2(A) and 2(B). FIG. 2(A) shows the relationship between a WE voltagerelative to the RE and the generation ratio between CO and H₂. FIG. 2(B)shows the relationship between the WE voltage relative to the RE and theenergy efficiency.

In general, H₂ is generated at an absolute potential of 0.11 V, which islower than the potential at which CO is generated. Therefore, in aregion of FIG. 2(A) where the voltage is low, the amount of generated H₂is relatively large. Hence, the generation ratio of CO/H₂ becomes low.When, in contrast, the voltage is high, the amount of generated CO canbe larger than that in a region where the voltage is low. Hence, thegeneration ratio of CO/H₂ is high. In other words, as indicated in FIG.2(A), the generation ratio of CO/H₂ becomes low when the WE voltage isset to be low relative to the RE and becomes high when the WE voltage isset to be high relative to the RE.

Meanwhile, the energy efficiency exhibits characteristics that differfrom the characteristics exhibited by the generation ratio of CO/H₂. Thefact that the WE voltage is low relative to the RE means that the inputenergy is small. In a region of FIG. 2(B) where the voltage is low,therefore, the energy efficiency increases with a decrease in thevoltage. Meanwhile, as described with reference to FIG. 2(A), thegeneration ratio of CO/H₂ is high in a region where the voltage is high.However, the amount of heat generated by CO (283 kJ/mol) is generallylarger than the amount of heat generated by H₂ (242 kJ/mol). Therefore,the amount of heat generated by the products increases with an increasein the generation ratio of CO/H₂. In other words, the energy efficiencyexhibits characteristics that bulge downward as shown in FIG. 2(B).

[Electrolysis in the Second Device 14]

Electrolysis reactions in the second device 14 will now be described incomparison with the electrolysis reactions in the first device 12. Whenthe potentiostat in the second device 14 is controlled so as to flow anelectric current between the WE and the CE, electrochemical reactionsoccur in the WE and CE as indicated by formulas (4) and (5) below:WE: 2H⁺+2e ⁻→H₂   (4)CE: 2H₂O →O₂+4H⁺+4e ⁻  (5)

The reaction indicated by formula (4) above is the same as the reactionindicated by formula (2), whereas the reaction indicated by formula (5)above is the same as the reaction indicated by formula (3).

FIG. 3(A) shows the relationship between the WE voltage relative to theRE and the generation ratio between CO and H₂. FIG. 3(B) shows therelationship between the WE voltage relative to the RE and the energyefficiency. As indicated by formula (4), only H₂ is generated on the WEin the second device 14. Therefore, the generation ratio of H₂ remainsconstant (=1.0) irrespective of the WE voltage relative to the RE, asshown in FIG. 3(A). Increasing the WE voltage relative to the REincreases the amount of generated H₂. Hence, the energy efficiency ofelectrolysis does not significantly vary as shown in FIG. 3(B).

[Power Distribution Control in the First Embodiment]

As is obvious from FIGS. 2 and 3, the generation ratio of CO/H₂ andenergy efficiency in the first device 12 vary with the WE voltagerelative to the RE, and the degree of such variation is greater thanthat in the second device 14. Therefore, when electric power derivedfrom natural energy is used as in the present embodiment, the firstdevice 12 is significantly affected by such variation. As such being thecase, the present embodiment exercises power distribution control so asto supply a steady-state portion of generated electric power to thefirst device 12 and supply the remaining variable portion to the seconddevice 14.

FIG. 4 shows an example of power distribution control that is providedby the present embodiment. The curve in FIG. 4 indicates changes innatural energy electric power. The present embodiment exercises powerdistribution control so as to supply steady-state power, which isindicated by a straight line below the curve, to the first device 12,and supply variable electric power, which is indicated by the curve, tothe second device 14. When such power distribution control is exercised,substantially constant power can be preferentially supplied to the firstdevice 12 in which energy efficiency increases with a decrease in thedegree of electric power variation, and variable electric power can besupplied to the second device 14 in which the influence upon energyefficiency is relatively small.

When power distribution control is exercised as described above,electric power can be supplied to the devices in accordance with theircharacteristics. Therefore, a decrease in energy efficiency can beeffectively reduced while making effective use of variable electricpower. Consequently, the system according to the present embodimentmakes it possible to produce HC with the enhanced energy efficiencyconcerning HC production.

In the first embodiment, which has been described above, the powercontrol distribution device 16 corresponds to the “power distributiondevice” according to the first aspect of the present invention; thefirst device 12 (CO/H₂ generating device) corresponds to the “mixed gasgenerating device” according to the first aspect of the presentinvention; and the controller in the power control distribution device16 corresponds to the “control device” according to the first aspect ofthe present invention.

Second Embodiment

A second embodiment of the present invention will now be described withreference to FIGS. 5(A) and 5(B). The second embodiment is characterizedin that mixture ratio feedback control is exercised as described laterwhen the above-described power distribution control is provided by thesystem according to the first embodiment. Elements of the system and themethod of power distribution control will not be redundantly describedbecause they are the same as those described in connection with thefirst embodiment.

[Mixture Ratio Feedback Control in the Second Embodiment]

In the first embodiment, which has been described earlier, powerdistribution control is exercised so as to suppress a decrease in energyefficiency. However, this power distribution control is exercised inconsideration of energy efficiency in an electrolysis process, which isa part of a HC production process, but is not exercised in considerationof energy efficiency in the overall process of HC production. It isunderstood that the energy efficiency is high during FT reaction whenthe mixture ratio of CO/H₂, that is, the mixture ratio between CO andH₂, which are reactants in the FT reaction, is 1/2.

In the present embodiment, therefore, the generation ratio of CO/H₂,that is, the generation ratio between CO and H₂, which aresimultaneously generated on the WE of the first device 12, is set to be1/2 in consideration of the energy efficiency during the FT reaction. Asdescribed with reference to FIG. 2(A), the CO/H₂ generation ratioprevailing on the WE depends on the WE voltage setting relative to theCE of the first device 12. Therefore, it is possible to preset a voltagevalue at which the generation ratio of CO/H₂ is 1/2.

However, when the above power distribution control is exercised,electric power remaining after the electric power supplied to the firstdevice 12 is subtracted from the electric power generated by the powergenerating device 10, is supplied to the second device 14. Therefore, H₂is generated in the second device 14 and introduced into the CO/H₂storage device 18 through the H₂ storage device 20. In other words, evenwhen the generation ratio of CO/H₂ is set to be 1/2 in the first device12, the mixture ratio between CO and H₂ in the CO/H₂ storage device 18varies with H₂ generated in the second device 14.

Hence, the present embodiment detects the mixture ratio between CO andH₂ in the CO/H₂ storage device 18 and exercises mixture ratio feedbackcontrol in which the result of the detection is fed back to the electricpower to be distributed. FIGS. 5(A) and 5(B) show examples of mixtureratio feedback control that is exercised in the present embodiment. Thebroken line in FIG. 5(A) indicates electric power to be supplied to thefirst device 12. The cumulative ratio of CO/H₂, which is shown in FIG.5(B), represents the mixture ratio between CO and H₂ in the CO/H₂storage device 18.

If the cumulative ratio of CO/H₂ is smaller than 1/2 as shown in FIG.5(B), a change is made to increase the electric power to be supplied tothe first device 12 as shown in FIG. 5(A). As explained with referenceto FIG. 2(A), the amount of generated CO can be increased by increasingthe WE voltage relative to the CE in the first device 12. In otherwords, when the electric power to be supplied to the first device 12 ischanged to increase, the generation ratio of CO/H₂ can be increased.

According to the above-described power distribution control, theelectric power to be supplied to the first device 12 can be changed inaccordance with the cumulative ratio of CO/H₂. Therefore, the mixtureratio of CO/H₂ in the CO/H₂ storage device 18 can be rendered close to1/2. It means that CO and H₂ in the CO/H₂ storage device 18 can bedirectly subjected to FT reaction. Hence, the energy efficiency in theoverall HC production process can be increased.

In the second embodiment, which has been described above, the CO/H₂storage device 18 corresponds to the “mixed gas storage device”according to the second aspect of the present invention; and thecontroller in the power control distribution device 16 corresponds tothe “feedback control device” according to the second aspect of thepresent invention.

Third Embodiment

A third embodiment of the present invention will now be described withreference to FIG. 6. The system according to the third embodiment isobtained by adding a H₂ power generating device, which generateselectric power by using H₂ as an energy source, to the system accordingto the first embodiment. The third embodiment is characterized in thatpower supply control is exercised as described later when theabove-described power distribution control is exercised. Elements of thesystem except for the H₂ power generating device and the method of powerdistribution control will not be redundantly described because they arethe same as those described in connection with the first embodiment.

[Power Supply Control in the Third Embodiment]

The first embodiment suppresses a decrease in energy efficiency byexercising power distribution control. However, as the system accordingto the first embodiment uses electric power derived from natural energy,the electric power to be supplied to the first device 12 maysignificantly decrease even when power distribution control is beingexercised.

As such being the case, the third embodiment uses a H₂ power generatingdevice 22 that is installed downstream of the H₂ storage device 20 togenerate electric power by using H₂. The third embodiment exercisespower supply control so that the electric power generated by the H₂power generating device 22 is supplied to the power control distributiondevice 16 when the amount of electric power generated by the powergenerating device 10 is decreased. This power supply control isexercised in accordance with a control signal from a controller (notshown). Electric power generation by the H₂ power generating device 22may be gas turbine power generation, steam turbine power generation,fuel cell power generation, or a combination of these.

Exercising power supply control as described above makes it possible tocompensate for changes in natural energy power generation. Therefore,stable electric power can be supplied to the first device 12. Further,when the power supply control is exercised, H₂ in the H₂ storage device20 does not flow toward the CO/H₂ storage device 18, but is consumed bythe H₂ power generating device 22. Consequently, the mixture ratiobetween CO and H₂ in the CO/H₂ storage device 18 can be adjusted toincrease the ratio of CO with an increased degree of freedom. As aresult, the first device 12 can be operated with ease.

In the third embodiment, which has been described above, the seconddevice 14 (H₂ generating device) corresponds to the “hydrogen generatingdevice” according to the third aspect of the present invention; and theH₂ power generating device 22 corresponds to the “hydrogen powergenerating device” according to the third aspect of the presentinvention.

Fourth Embodiment

A fourth embodiment of the present invention will now be described withreference to FIGS. 7(A) and 7(B). The fourth embodiment is characterizedin that power supply control and mixture ratio feedback control areexercised as described later when the above-described power distributioncontrol is provided by the system according to the third embodiment.Elements of the system and the method of power distribution control willnot be redundantly described because they are the same as thosedescribed in connection with the third embodiment.

[Power Supply Control and Mixture Ratio Feedback Control in the FourthEmbodiment]

When the amount of electric power generated by the power generatingdevice 10 is decreased, the third embodiment compensates for changes innatural energy power generation by exercising power supply control inwhich the electric power generated by the H₂ power generating device 22is supplied to the power control distribution device 16. In contrast,the present embodiment exercises power supply control in which theelectric power generated by the H₂ power generating device 22 isconstantly supplied to the power control distribution device 16. Thispower supply control is exercised in accordance with a control signalfrom a controller (not shown). Further, the present embodiment detectsthe mixture ratio between CO and H₂ in the CO/H₂ storage device 18 andexercises mixture ratio feedback control in which the result of thedetection is fed back to the electric power to be distributed, as is thecase with the second embodiment.

FIGS. 7(A) and 7(B) show examples of power supply control and mixtureratio feedback control that are exercised by the present embodiment. Thebroken line in FIG. 7(A) indicates electric power to be supplied to thefirst device 12. The cumulative ratio of CO/H₂, which is shown in FIG.7(B), represents the mixture ratio between CO and H₂ in the CO/H₂storage device 18.

When power supply control is initiated at point S shown in FIG. 7(A),changes in natural energy electric power can be compensated for to someextent. Therefore, an alterable upper-limit value of electric power canbe increased during mixture ratio feedback control. Hence, if thecumulative ratio of CO/H₂ is smaller than 1/2 as shown in FIG. 7(B), achange is made to increase the electric power to be supplied to thefirst device 12 as shown in FIG. 7(A). Consequently, the generationratio of CO/H₂ can be increased until it is close to 1/2.

According to the above-described power supply control and mixture ratiofeedback control, the electric power to be supplied to the first device12 can be changed in accordance with the cumulative ratio of CO/H₂ whilecompensating for changes in the natural energy electric power.Therefore, the alterable upper-limit value of electric power can beincreased. Thus, the mixture ratio of CO/H₂ in the CO/H₂ storage device18 can be accurately rendered close to 1/2. Consequently, CO and H₂ inthe CO/H₂ storage device 18 can be directly subjected to FT reaction.This makes it possible to further increase the energy efficiency in theoverall HC production process.

Fifth Embodiment

A fifth embodiment of the present invention will now be described withreference to FIG. 8. The fifth embodiment is characterized in that powerdistribution control is exercised as described later with the H₂generating device according to the first embodiment replaced by alater-described CO/H₂ generating device. Elements of the system exceptfor the CO/H₂ generating device will not be redundantly describedbecause they are the same as those described in connection with thefirst embodiment.

[Power Distribution Control in the Fifth Embodiment]

The second device 14 used in the present embodiment is the same CO/H₂generating device as the first device 12. An electrical storage deviceis combined with a power supply section of the second device 14.Therefore, changes in the electric power to be supplied to the seconddevice 14 can be smoothed to some extent by the electrical storagedevice although a certain loss occurs due to electric power input andoutput. FIG. 8 shows an example of power distribution control that isprovided by the present embodiment. The curve in FIG. 8 indicateschanges in natural energy electric power. The present embodimentexercises the same power distribution control as the first embodiment.In the present embodiment, however, smoothed steady-state electric powerindicated by the one-dot chain line in FIG. 8 is supplied to the seconddevice 14 from the electrical storage device. Therefore, CO and H₂ canbe generated with high energy efficiency not only in the first device 12but also in the second device 14.

In the fifth embodiment, which has been described above, the seconddevice 14 (CO/H₂ generating device) corresponds to the “mixed gasgenerating device” according to the fifth aspect of the presentinvention; and the electrical storage device in the second device 14corresponds to the “charge/discharge device” according to the fifthaspect of the present invention.

Sixth Embodiment

A sixth embodiment of the present invention will now be described withreference to FIG. 9. The sixth embodiment is characterized in that powerdistribution control and electrolytic solution supply control areexercised as described later with the H₂ generating device according tothe first embodiment replaced by a later-described blower/liquid supplydevice and with the H₂ storage device 20 replaced by a later-describedatmospheric CO₂ recovery device. Elements of the system except for theabove-mentioned devices will not be redundantly described because theyare the same as those described in connection with the first embodiment.

As explained in connection with the first embodiment, the first device12 includes an electrolytic tank that is filled with an electrolyticsolution in which CO₂ is dissolved. Therefore, when an electric currentflows between the WE and the CE, CO₂ undergoes electrolysis to generateCO. However, the amount of CO₂ in the electrolytic solution decreases asCO is generated. To steadily generate CO, therefore, it is necessary toadditionally introduce CO₂ into the electrolytic tank from the outside.Hence, as shown in FIG. 9, the present embodiment includes theblower/liquid supply device as the second device 14.

The second device 14 is combined with an atmospheric CO₂ recovery device24 so as to perform a function of supplying an electrolytic solution tothe first device 12. When functioning as the liquid supply device, thesecond device 14 is a liquid supply pump that supplies a CO₂ absorbingliquid/electrolytic solution to the first device 12 through theatmospheric CO₂ recovery device 24. In this instance, the atmosphericCO₂ recovery device 24 functions as a storage tank that temporarilystores the CO₂ absorbing liquid/electrolytic solution. When functioningas the blower, in contrast, the second device 14 is a blower pump thatintroduces CO₂ in the atmosphere into the atmospheric CO₂ recoverydevice 24. In this instance, the atmospheric CO₂ recovery device 24contains the CO₂ absorbing liquid/electrolytic solution, and functionsas a liquid supply pump that supplies to the first device 12 the CO₂absorbing liquid/electrolytic solution in which CO₂ is dissolved.

[Power Distribution Control and Electrolytic Solution Supply Control inthe Sixth Embodiment]

Meanwhile, supplying variable electric power to the second device 14 (orthe atmospheric CO₂ recovery device 24) varies the amount of CO₂ to bedissolved in the absorbing liquid/electrolytic solution within theatmospheric CO₂ recovery device 24 and the amount of CO₂ absorbingliquid/electrolytic solution to be supplied to the first device 12.Thus, the changes in the amount of CO₂ and in the amount of CO₂absorbing liquid/electrolytic solution may affect the generation ratioof CO/H₂ and energy efficiency in the first device 12. However, theinfluence of the changes in the amount of CO₂ and in the amount of CO₂absorbing liquid/electrolytic solution is smaller than the influence ofchanges in the electric power to be supplied to the first device 12.

As such being the case, the present embodiment exercises powerdistribution control so as to supply a steady-state portion of electricpower generated by the power generating device 10 to the first device 12and supply the remaining variable portion to the second device 14 (orthe atmospheric CO₂ recovery device 24). In addition, the presentembodiment exercises electrolytic solution supply control so as tocollectively supply the electrolytic solution to the first device 12when a certain CO₂ concentration is reached in the atmospheric CO₂recovery device 24. This electrolytic solution supply control isexercised in accordance with a control signal from a controller (notshown). Exercising the above-described power distribution control andelectrolytic solution supply control makes it possible to minimize theinfluence of the variable electric power upon the generation ratio ofCO/H₂ and energy efficiency.

As described above, the system according to the present embodiment canadditionally supply CO₂ to the first device 12. Therefore, the firstdevice 12 can steadily generate CO. Further, when the power distributioncontrol and electrolytic solution supply control according to thepresent embodiment are exercised, CO and H₂ can be generated whileminimizing the influence of the variable electric power upon thegeneration ratio of CO/H₂ and energy efficiency.

In the sixth embodiment, which has been described above, the seconddevice 14 (blower/liquid supply device) and the atmospheric CO₂ recoverydevice 24 correspond to the “carbon dioxide supply device” according tothe sixth aspect of the present invention.

Further, in the sixth embodiment, which has been described above, thesecond device 14 (liquid supply device) or the atmospheric CO₂ recoverydevice 24 operated when the second device 14 functions as a blowerdevice corresponds to the “carbon dioxide recovery device” according tothe seventh aspect of the present invention.

Furthermore, in the sixth embodiment, which has been described above,the second device 14 (blower device) corresponds to the “atmospheric airintroduction device” according to the eighth aspect of the presentinvention; and the atmospheric CO₂ recovery device 24 operated when thesecond device 14 functions as a blower device corresponds to the “liquidsupply device” according to the eighth aspect of the present invention.

Seventh Embodiment

A seventh embodiment of the present invention will now be described withreference to FIG. 10. The system according to the seventh embodiment ischaracterized in that the blower/liquid supply device according to thesixth embodiment is replaced by a liquid supply device, and that anabsorbing liquid storage tank and a hydraulic turbine generator areadded between the liquid supply device and the atmospheric CO₂ recoverydevice 24, and further that a CO₂ absorbing liquid/electrolytic solutioncirculates between the above-mentioned added hardware and the firstdevice 12. The system according to the present embodiment is alsocharacterized in that later-described power supply control is exercisedwhen the earlier-described power distribution control and electrolyticsolution supply control are exercised. Elements of the system except forthe liquid supply device, absorbing liquid storage tank, and hydraulicturbine generator, and the methods of power distribution control andelectrolytic solution supply control will not be redundantly describedbecause they are the same as those described in connection with thesixth embodiment.

As described in connection with the sixth embodiment, the amount of CO₂in the electrolytic solution decreases as CO is generated. To steadilygenerate CO, it is necessary to additionally introduce CO₂ into theelectrolytic tank from the outside. Hence, as shown in FIG. 10, thepresent embodiment includes the liquid supply device as the seconddevice 14. The second device 14 is combined with an absorbing liquidstorage tank 26, a hydraulic turbine generator 28, and the atmosphericCO₂ recovery device 24 to perform a function of supplying the CO₂absorbing liquid/electrolytic solution to the first device 12.

More specifically, the second device 14 functions as a liquid lift pumpthat lifts the CO₂ absorbing liquid/electrolytic solution to theabsorbing liquid storage tank 26, which is positioned higher than thefirst device 12. The absorbing liquid storage tank 26 functions as astorage tank that temporarily stores the CO₂ absorbingliquid/electrolytic solution. The hydraulic turbine generator 28functions as a hydraulic power generation device that generates electricpower by allowing a turbine to be rotated by the potential energy of theCO₂ absorbing liquid/electrolytic solution when it flows downward bygravity from the absorbing liquid storage tank 26. The atmospheric CO₂recovery device 24 functions as a liquid supply pump that supplies theCO₂ absorbing liquid/electrolytic solution to the first device 12. Asthe first device 12 is connected to the second device 14, the CO₂absorbing liquid/electrolytic solution flows again into the seconddevice 14 after being discharged from the first device 12.

Further, as described in connection with the sixth embodiment, supplyingvariable electric power to the second device 14 varies the amount of CO₂absorbing liquid/electrolytic solution to be supplied to the firstdevice 12. Therefore, changes in the amount of CO₂ absorbingliquid/electrolytic solution may affect the generation ratio of CO/H₂and energy efficiency in the first device 12. Hence, the absorbingliquid storage tank 26 used in the present embodiment has a sufficientvolumetric capacity. This makes it possible to absorb the changes in theamount of CO₂ absorbing liquid/electrolytic solution, which occur whenvariable electric power is supplied. Consequently, the influence ofvariable electric power upon the generation ratio of CO/H₂ and energyefficiency can be successfully eliminated.

[Power Supply Control in the Seventh Embodiment]

Moreover, as described in connection with the third embodiment, theelectric power to be supplied to the first device 12 may significantlydecrease while power distribution control is being exercised. Therefore,when the amount of electric power generated by the power generatingdevice 10 is decreased, the present embodiment exercises power supplycontrol so as to supply the electric power generated by the hydraulicturbine generator 28 to the power control distribution device 16. Thispower supply control is exercised in accordance with a control signalfrom a controller (not shown). Exercising power supply control in themanner described above makes it possible to compensate for changes innatural energy power generation. Thus, electric power can be steadilysupplied to the first device 12. Consequently, the present embodimentprovides substantially the same advantages as the third embodiment.

As described above, the system according to the present embodiment canadditionally supply CO₂ to the first device 12. Therefore, the firstdevice 12 can steadily generate CO. Further, the absorbing liquidstorage tank 26 used in the system according to the present embodimenthas a sufficient volumetric capacity. Therefore, the influence ofvariable electric power upon the generation ratio of CO/H₂ and energyefficiency can be successfully eliminated. In addition, the presentembodiment exercises power supply control in such a manner as tocompensate for changes in natural energy power generation. Thus,electric power can be steadily supplied to the first device 12.Consequently, the mixture ratio between CO and H₂ in the CO/H₂ storagedevice 18 can be adjusted to increase the ratio of CO with an increaseddegree of freedom. As a result, the first device 12 can be operated withease.

In the seventh embodiment, which has been described above, the seconddevice 14 (liquid supply device), the absorbing liquid storage tank 26,the hydraulic turbine generator 28, and the atmospheric CO₂ recoverydevice 24 correspond to the “carbon dioxide supply device” according tothe sixth aspect of the present invention.

Further, in the seventh embodiment, which has been described above, theatmospheric CO₂ recovery device 24 corresponds to the “carbon dioxiderecovery device” according to the seventh aspect of the presentinvention.

Furthermore, in the seventh embodiment, which has been described above,the absorbing liquid storage tank 26 corresponds to the “electrolyticsolution storage device” according to the ninth aspect of the presentinvention; the hydraulic turbine generator 28 corresponds to the“hydraulic power generation device” according to the ninth aspect of thepresent invention; and the atmospheric CO₂ recovery device 24corresponds to the “liquid supply device” according to the ninth aspectof the present invention.

Eighth Embodiment

An eighth embodiment of the present invention will now be described withreference to FIG. 11. The eighth embodiment is characterized in that theblower/liquid supply device and atmospheric CO₂ recovery deviceaccording to the sixth embodiment are respectively replaced by a CO₂absorbent regeneration device and a CO₂ dissolution device. Elements ofthe system except for the CO₂ absorbent regeneration device and CO₂dissolution device, and the method of electrolytic solution supplycontrol will not be redundantly described because they are the same asthose described in connection with the sixth embodiment.

As described in connection with the sixth embodiment, the amount of CO₂in the electrolytic solution decreases as CO is generated. To steadilygenerate CO, it is necessary to additionally introduce CO₂ into theelectrolytic tank from the outside. Hence, as shown in FIG. 11, thepresent embodiment includes the CO₂ absorbent regeneration device as thesecond device 14. The second device 14 is combined with a CO₂dissolution device 30 to perform a function of supplying theelectrolytic solution to the first device 12. More specifically, thesecond device 14 includes a heater (not shown), a water addition device(not shown), and a CO₂ absorbent (not shown) having CO₂ absorptioncharacteristics (e.g., sodium hydroxide or calcium hydroxide). When theCO₂ absorbent is heated by the heater, CO₂ is removed from the CO₂absorbent. When the water addition device adds water to the CO₂absorbent, its CO₂ absorption characteristics are regenerated.Therefore, when the removal of CO₂ and the regeneration of CO₂absorption characteristics are repeated in the second device 14, CO₂ canbe separated from atmospheric air and supplied to the CO₂ dissolutiondevice 30. Further, the CO₂ dissolution device 30 contains the CO₂absorbing liquid/electrolytic solution, and functions as a liquid supplypump so that CO₂ supplied from the second device 14 is dissolved in theCO₂ absorbing liquid/electrolytic solution and supplied to the firstdevice 12.

[Power Distribution Control in the Eighth Embodiment]

When variable electric power is supplied to the second device 14, thethermal dose per unit time varies. However, the CO₂ absorbent has a heatcapacity. Therefore, even when the thermal dose per unit time varies,the CO₂ absorbent can reach a regeneration temperature with time andgenerate CO₂. As such being the case, the present embodiment exercisespower distribution control so as to supply a steady-state portion ofelectric power generated by the power generating device 10 to the firstdevice 12 and supply the remaining variable portion to the second device14. When the above-described power distribution control is exercised,the variable electric power can be effectively used to generate CO₂.

As described above, the system according to the present embodiment canadditionally supply CO₂ to the first device 12. Therefore, the firstdevice 12 can steadily generate CO. Further, when the power distributioncontrol according to the present embodiment is exercised, the variableelectric power can be effectively used to generate CO₂.

In the eighth embodiment, which has been described above, the seconddevice 14 (CO₂ absorbent regeneration device) and the CO₂ dissolutiondevice 30 correspond to the “carbon dioxide supply device” according tothe sixth aspect of the present invention.

Further, in the eighth embodiment, which has been described above, theCO₂ dissolution device 30 corresponds to the “carbon dioxide recoverydevice” according to the seventh aspect of the present invention.

Furthermore, in the eighth embodiment, which has been described above,the second device 14 (CO₂ absorbent regeneration device) corresponds tothe “carbon dioxide absorption/regeneration device” according to thetenth aspect of the present invention.

Ninth Embodiment

A ninth embodiment of the present invention will now be described withreference to FIG. 12. The ninth embodiment is characterized in that theblower/liquid supply device according to the sixth embodiment and theatmospheric CO₂ recovery device 24 are replaced by a later-described CO₂pressure pump and a high-pressure CO₂ storage tank, respectively, andthat power supply control is exercised as described later when theabove-described power distribution control and electrolytic solutionsupply control are exercised. Elements of the system except for the CO₂pressure pump and high-pressure CO₂ storage tank, and the methods ofpower distribution control and electrolytic solution supply control willnot be redundantly described because they are the same as thosedescribed in connection with the sixth embodiment.

As described in connection with the sixth embodiment, the amount of CO₂in the electrolytic solution decreases as CO is generated. To steadilygenerate CO, it is necessary to additionally introduce CO₂ into theelectrolytic tank from the outside. Hence, as shown in FIG. 12, thepresent embodiment includes the CO₂ pressure pump as the second device14. The second device 14 is combined with a low-pressure CO₂ storagetank 32, an atmospheric CO₂ recovery device 34, and a high-pressure CO₂storage tank 36 to perform a function of supplying the CO₂ absorbingliquid/electrolytic solution to the first device 12. The high-pressureCO₂ storage tank 36 contains the CO₂ absorbing liquid/electrolyticsolution. The CO₂ absorbing liquid/electrolytic solution absorbs CO₂when pressurized by the second device 14, and is supplied to the firstdevice 12 by a liquid supply pump (not shown). Further, the CO₂recovered by the atmospheric CO₂ recovery device 34 and temporarilystored in the low-pressure CO₂ storage tank 32 is pressurized by thesecond device 14.

[Power Supply Control in the Ninth Embodiment]

When variable electric power is supplied to the second device 14, thedrive of the CO₂ pressure pump varies. Therefore, when electric powerincreases, the present embodiment causes the CO₂ pressure pump tofunction as a blower pump and permits the high-pressure CO₂ storage tank36 to absorb CO₂. Further, when electric power decreases, the presentembodiment exercises power supply control so as to supply electric powerto the power control distribution device 16 by using part of thepressure from the high-pressure CO₂ storage tank 36 to drive the CO₂pressure pump in a reverse direction and operate it as a powergenerator. This power supply control is exercised in accordance with acontrol signal from a controller (not shown). Exercising power supplycontrol as described above makes it possible to compensate for changesin natural energy power generation. Therefore, stable electric power canbe supplied to the first device 12. Consequently, the present embodimentprovides substantially the same advantages as the third embodiment.

As described above, the system according to the present embodiment canadditionally supply CO₂ to the first device 12. Therefore, the firstdevice 12 can steadily generate CO. Further, the present embodimentexercises power supply control in such a manner as to compensate forchanges in natural energy power generation. Thus, stable electric powercan be supplied to the first device 12. Consequently, the mixture ratiobetween CO and H₂ in the CO/H₂ storage device 18 can be adjusted toincrease the ratio of CO with an increased degree of freedom. As aresult, the first device 12 can be operated with ease.

In the ninth embodiment, which has been described above, the seconddevice 14 (CO₂ pressure pump), the low-pressure CO₂ storage tank 32, theatmospheric CO₂ recovery device 34, and the high-pressure CO₂ storagetank 36 correspond to the “carbon dioxide supply device” according tothe sixth aspect of the present invention.

Further, in the ninth embodiment, which has been described above, thehigh-pressure CO₂ storage tank 36 corresponds to the “carbon dioxiderecovery device” according to the seventh aspect of the presentinvention.

Furthermore, in the ninth embodiment, which has been described above,the second device 14 (CO₂ pressure pump) corresponds to the “rotatingelectrical machine” according to the eleventh aspect of the presentinvention; and the high-pressure CO₂ storage tank 36 corresponds to the“carbon dioxide recovery device” according to the eleventh aspect of thepresent invention.

Description Of Reference Numerals

10 power generating device

12 first device

14 second device

16 power control distribution device

18 CO/H₂ storage device

20 H₂ storage device

22 H₂ power generating device

24, 34 atmospheric CO₂ recovery device

26 absorbing liquid storage tank

28 hydraulic turbine generator

30 CO₂ dissolution device

32 low-pressure CO₂ storage tank

36 high-pressure CO₂ storage tank

The invention claimed is:
 1. A fuel production system comprising: apower generating device that generates variable electric power; a powerdistribution device that is connected to the power generating device todistribute electric power to a plurality of electrical loads; a mixedgas generating device that is one of the electrical loads and performselectrolysis on water and carbon dioxide upon receipt of electric powerdistributed by the power distribution device to generate a mixed gasmade of hydrogen and carbon monoxide; and a control device that controlsthe power distribution device so as to supply predetermined electricpower to the mixed gas generating device, wherein the predeterminedelectric power is lower than the minimum power generated by the powergenerating device within a preselected period of time.
 2. The fuelproduction system according to claim 1, further comprising: a mixed gasstorage device that is connected to the mixed gas generating device tostore the mixed gas; and a feedback control device that providesfeedback control of the predetermined electric power to ensure that thesubstance quantity ratio between hydrogen and carbon monoxide in themixed gas storage device coincides with a preselected ratio.
 3. The fuelproduction system according to claim 1, further comprising: a hydrogengenerating device that is one of the electrical loads and generateshydrogen upon receipt of electric power distributed by the powerdistribution device; and a hydrogen power generating device thatgenerates electric power by using hydrogen generated by the hydrogengenerating device.
 4. The fuel production system according to claim 3,wherein, if the electric power generated by the power generating deviceis lower than the predetermined electric power while the control devicecontrols the power distribution device to supply the predeterminedelectric power to the mixed gas generating device, the hydrogen powergenerating device supplies the generated electric power to the powerdistribution device.
 5. The fuel production system according to claim 1,further comprising: a charge/discharge device that is one of theelectrical loads and capable of charging and discharging electric powerdistributed by the power distribution device; and a mixed gas generatingdevice that generates a mixed gas made of hydrogen and carbon monoxideby performing electrolysis on water and carbon dioxide by using electricpower from the charge/discharge device.
 6. The fuel production systemaccording to claim 1, further comprising: a carbon dioxide supply devicethat is one of the electrical loads, recovers carbon dioxide fromatmospheric air upon receipt of electric power distributed by the powerdistribution device, and supplies the recovered carbon dioxide to themixed gas generating device.
 7. The fuel production system according toclaim 6, wherein the carbon dioxide supply device includes a carbondioxide recovery device that contains an electrolytic solution havingcarbon dioxide absorption characteristics.
 8. The fuel production systemaccording to claim 7, wherein the carbon dioxide supply device includesan atmospheric air introduction device that introduces atmospheric airinto the carbon dioxide recovery device, and a liquid supply device thatsupplies the electrolytic solution in the carbon dioxide recovery deviceto the mixed gas generating device.
 9. The fuel production systemaccording to claim 7, further comprising: an electrolytic solutionstorage device that is disposed downstream and upward of the carbondioxide recovery device to temporarily store an electrolytic solutiondischarged from the mixed gas generating device; a hydraulic powergeneration device that includes a turbine rotated by an electrolyticsolution dropped from the electrolytic solution storage device, causesthe rotated turbine to generate electric power, and if the electricpower generated by the power generating device is lower than thepredetermined electric power, supplies the generated electric power tothe power distribution device; and a liquid supply device that suppliesthe electrolytic solution dropped from the electrolytic solution storagedevice to the mixed gas generating device.
 10. The fuel productionsystem according to claim 7, wherein the carbon dioxide supply deviceincludes a carbon dioxide absorption/regeneration device that ispositioned upstream of the carbon dioxide recovery device, and containsan absorbent that has carbon dioxide absorption characteristics,discharges absorbed carbon dioxide when heated, and regenerates thecarbon dioxide absorption characteristics when watered.
 11. The fuelproduction system according to claim 7, wherein the carbon dioxidesupply device includes a rotating electrical machine disposed upstreamof the carbon dioxide recovery device; and wherein the rotatingelectrical machine includes a turbine, functions as a pressure pump thatlets the turbine rotate to compress carbon dioxide and introduce thecompressed carbon dioxide into the carbon dioxide recovery device, andif the electric power generated by the power generating device is lowerthan the predetermined electric power, functions as a power generatorthat generates electric power by allowing the compressed carbon dioxidein the carbon dioxide recovery device to rotate the turbine in a reversedirection and supplies the generated electric power to the powerdistribution device.
 12. The fuel production system according to claim1, wherein the power generating device includes at least one of a solarphotovoltaic power generation device, a solar thermal power generationdevice, a wind power generation device, a tidal power generation device,and a geothermal power generation device.